The present invention relates to a backup technology for data in a storage system or a server, and more specifically to a technology of asynchronous data update between plural sites.
Databases and web sites avoid data redundancy by taking a backup and storing the backup data in physically different storage system. For instance, data of a site that is currently in use (hereinafter referred to as currently-used site) is transferred to a storage system on a site located in a geographically remote place (hereinafter referred to as remote site) and the data is updated so that the backup data on the remote site can be used to avoid losing data of the currently-used site over calamities such as earthquake in case the effectiveness of the currently-used site is impaired.
Such data backup systems known to this point are divided into synchronous backup systems (EP 0671686 A1) with which a data update on a remote site is synchronous with a data update on a currently-used site and asynchronous backup systems (EP 0672985 A1) with which a data update on a currently-used site is followed by a data update on a remote site.